Ampmeter will not 'excite'
 

My ampmeter was working just fine, and now it refuses to 'excite' to positive when I start the engine and rev it up. The needle stays slightly negative no matter what I do.

I assumed the ampmeter went bad on me, so I installed another new one. No change. So I installed yet-another new one. No change.

My car has a 12-volt system. As far as I know there's nothing wrong with the alternator. Also, the electrical connection to the alternator is tight, as are the connections to the back of the ampmeter.

It certainly seems that the ampmeter itself is OK and that its faulty performance is being caused by something in the electrical system.

I have no clue what to do next. I welcome any advice you may have to offer.

Thanks.

Re: Ampmeter will not 'excite'
 

The first thing I would do, is assume that the ammeter is working and that you have a problem. After all, the reason for the ammeter is to show you that a problem is occurring.

The fact that the you have a discharge indicates that the alternator isn't working. What info tells you that it's O.K. ?

Loose belt maybe ?

Marc

Re: Ampmeter will not 'excite'
 

amp meter does not excite , alt's do . test it with a volt meter or turn your high beams on tro see how bright they are . you can also test to see if the batt is getting voltage .

Re: Ampmeter will not 'excite'
 

I recently had the same problem. I took the alternator to the electrical shop. It took about 2 minutes to determine that the alternator needed repairs. They fixed it the same day for $38.05 including tax and took me half hour to pick it up and 10 minutes to reinstall it. It's been working properly ever since. If the problem hadn't been the alternator there would have been no charge for the diagnosis.

Re: Ampmeter will not 'excite'
 

Step on the brake or turn on the lights, if the ammeter shows a discharge its fine.

The problem is probably the alternator as said. If its a Delco, many have a 'D' shaped hole in the rear case. While the engine is running if the D hole is there insert a screwdriver and see if it then charges. If it does, the regulator is bad.

Re: Ampmeter will not 'excite'
 

Odds are 3 ammeters cannot be broken in the same manner thereby producing the same result..

Re: Ampmeter will not 'excite'
 

I believe you gentlemen have identified my problem. I hadn't considered the alternator, but I now see that it's the likely culprit. I'll take it to NAPA tomorrow and have them test it. Thanks for your assistance!

Re: Ampmeter will not 'excite'
 

when testing a alt. put a volt meter across the battery at idle it should be @ 13 volts amp meters are good for generators but volt meters are best for alternators there not hard to repair with a ohm meter you can test the more apt to fail parts like diode trio or rectifier bridge also as was stated about the d hole in the back shorting it out puts the unit in full output and if it charges its time to replace the voltage reg.

Re: Ampmeter will not 'excite'
 

Alternators DO go BAD! Jist go stand at your local Car Quest for an hour & see how MANY are TOTED IN!!
As Chief would say,"THEY'RE A WEAR & TEAR ITEM"!!
Bill W.

Re: Ampmeter will not 'excite'
 

You can read up on all the different ways to test an Alt but the easiest I feel is to take it out and bring it to a shop.

Re: Ampmeter will not 'excite'
 

At night just turn the lights on with the engine at fast idle, then kill the engine. If the lights dim as the engine dies, the alternator is working.

Better yet, just connect a volt meter to the alternator output and see if the voltage goes up after the engine is started. If not, then it needs to be repaired.

Re: Ampmeter will not 'excite'
 

My gosh Tom , how simple is that! Another of whyever-didn't-I-think-of-that moments! Thank you.

Re: Ampmeter will not 'excite'
 

In addition, if the lights dim "a lot" when you stop the motor, then the battery is getting old.

Good general test.

Marc